A thyroid scan is an image made of the thyroid gland after you have swallowed a small amount of radioactive iodine. Because the thyroid naturally uses iodine to produce some of its hormones, it absorbs the radioactive substance. This substance emits energy and allows the image to be made. The image will show if the thyroid gland is enlarged and overactive.
Before the scan, you will be given a small amount of radioactive iodine by pill, or by injection. Your thyroid will need time to absorb the iodine – from fifteen minutes to six hours – depending on your symptoms and whether the iodine was given by pill or by injection.
Once the iodine has been absorbed, you will lie on your back on a table, under a scanning device. The device creates images from the energy emitted by the radioactive iodine. You will need to lie still for about five minutes in order for the scanner to make clear images. The entire scan will take about a half-hour.
A functioning thyroid nodule, which can cause your thyroid gland to overproduce hormones (hyperthyroidism), shows up on the scan as a "hot" area. Non-functioning nodules show up as holes in the scan, or "cold" areas. Hot nodules are almost always benign (non-cancerous), while a small percentage of cold nodules can form cancer. About five percent of thyroid nodules may be malignant, or cancerous.
The test causes no pain. You can resume your normal activities following the test.
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